1. Field of the Invention
In the field of art to which the claimed invention pertains is solid-bed adsorptive separation. More specifically, the claimed invention relates to a process for the separation of 1,3-butadiene from a feed mixture comprising 1,3-butadiene and at least one other C.sub.4 unsaturate which process employs a solid adsorbent which selectively removes 1,3-butadiene from the feed mixture.
2. Description of the Prior Art
It is well known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbons species from mixtures thereof. In particular, the separation of normal paraffins from branched chained paraffins can be accomplished by using the type A zeolites which have pore openings from 3 to 5 Angstroms. Such a separation process is disclosed for example in U.S. Pat. Nos. 2,985,589 and 3,201,491. These adsorbents allow a separation based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to be passed into the cavities within the crystalline aluminosilicate adsorbent, while excluding the larger or branched chain molecules.
U.S. Pat. Nos. 3,265,750 and 3,510,423, for example, disclose processes in which larger pore diameter zeolites such as the type X or type Y structured zeolites can be used to separate olefinic hydrocarbons.
In addition to separating hydrocarbon types, the type X or type Y zeolite have also been employed in processes to separate individual hydrocarbon isomers. In the process described in U.S. Pat. Nos. 3,668,730, 3,668,732, 3,626,020, and 3,686,342, for example, they are used to separate desired xylene isomers; in U.S. Pat. No. 3,668,267 they are used to separate particular alkyl substituted naphthalenes.
The present invention relates to a process for the separation of 1,3-butadiene from a feed mixture comprising 1,3-butadiene and at least one other C.sub.4 unsaturate with a particular zeolitic adsorbent.
I have found that adsorbents comprising type X or type Y zeolites, which have been found to work equally well in many other adsorptive processes, are not equivalent for use in this process. I have found that adsorbents comprising type X zeolites containing sodium or potassium at the exchangeable cationic sites possess both good adsorptive capacity and selectivity for 1,3-butadiene as well as low polymerization activity for 1,3-butadiene and are therefore suitable for use in my process. Furthermore the polymerization activity of the adsorbent can be further reduced by employing a particular adsorbent preparation procedure. In a preferred embodiment my process employs the adsorbent so produced in combination with operating conditions which include the liquid phase and a rather low temperature range of from about 25.degree. to about 75.degree. C. to minimize the polymerization of 1,3-butadiene and prolong the useful life of the adsorbent.